1. Field of the Invention
This invention generally relates to a thermal protector for a hermetic refrigeration compressor having a housing in which an electric motor and a compressing means are enclosed with refrigerant gas flowing therein, and more particularly to a structure for mounting the thermal protector responsive to heat generated from the motor or the compressing means in an abnormal condition to cut off the motor current.
2. Description of the Prior Art
Hermetic refrigeration compressors have conventionally been incorporated with a bimetal protector device, for example, for protecting a motor and the like against overheating of the motor, compressor or the like in an abnormal condition. The protector device is mounted on an outer wall of an enclosed housing of the compressor or closely banded together with coils of the motor by strings, as is well known in the art.
Japanese Published Utility Model Application (Kokoku) No. 52-6801 (1977) discloses a protective relay which is screwed into a hole formed in an enclosed housing so as to be engaged with a coil end of the motor. Japanese Published Utility Model Application (Kokai) No. 63-10763 (1988) discloses an overload protector inserted in a hole formed at the motor side of the housing to be airtightly secured therein.
Japanese Published Patent Application (Kokai) No. 59-67853 (1984) discloses a protector provided between an airtight terminal assembly and an electric motor in a hermetic housing. Japanese Published Patent Application (Kokai) No. 62-296739 (1987) discloses an internal protector enclosed in a socket mounted on an airtight casing.
The above-mentioned prior art references have the following problems. That is, the closed housing is formed from a metal in the construction that the protector is mounted on the outer wall of the airtight housing or that the overload protector is airtightly secured into the housing. Accordingly, since the thermal conductivity of the enclosed housing is relatively large, heat accumulated in the housing wall is radiated as the result of its contact with outside air and the like. Consequently, since heat induced in the housing is absorbed by the housing wall before reaching the protector, the response of the protector to the heat is retarded. Thus, it takes much time for the temperature increase in the housing to be transmitted to the protector and accordingly, a sufficient protecting operation cannot be expected against sudden or steep temperature increase.
In the construction that the protector is banded together with the motor coils by the strings, sheathing for electrical insulation from the coils is necessitated. Consequently, mounting the protector is troublesome. Furthermore, heat is absorbed into the coils in an abnormal condition of the compressor wherein the temperature of the compressing means exceeds that of the motor coils. In this case, the thermal responsiveness of the protector is lowered. Even when the temperature is increased such that the refrigerant is deteriorated, transmission of the heat to the thermal protector causes a certain time lag.
In the construction that the protector is provided between the airtight terminal assembly and the electric motor, a sufficient insulation distance is required among parts of the protector in order that the motor is directly controlled by the protector. Consequently, it is difficult to render the protector small-sized.
Furthermore, in the construction that the internal protector is enclosed in the socket, an exclusive or dedicated socket needs to be provided and the thermal responsiveness of the protector is lowered by the socket having a certain heat insulation.
Furthermore, in the above-mentioned protector responsive to both the temperature and the overcurrent, its construction is complicated and accordingly, it is difficult to render the protector small-sized.